Q: WHY SHOULD YOU USE A CHARGE CONTROLLER TO CHARGE YOUR LEAD ACID POWERPACK BATTERY WITH SOLAR / WIND / PEDAL POWER?
Short & Easy Answer: Because if you pedal too fast and generate too high of a voltage from your bike generator, you could dramatically shorten the life of your battery / powerpack.
Longer more technical answer: Your battery / power pack has a limit on how high of a voltage it can see while charging. One term to describe this voltage is called the "Peak Charge Voltage". If you pedal too fast and generate too high of a voltage, then you could exceed the peak charge voltage and supply your battery with too much current. This would damage the cells inside and affect their ability to take a charge.
In most cases the peak charge voltage for a lead acid / AGM (absorbed glass mat) battery / powerpack is somewhere near 14.8V DC (V= Volts DC= Direct Current).
This NC25A charge controller has a diversion load output (diversion load slows down or provides a "braking" function to a wind turbine or over enthusiastic cyclist). I like hooking the diversion load up to one or two of these 1000-Watt work light stands. When the charge controller switches into diversion load mode, the current from the pedal power or wind turbine generator will be routed into the two 1000 W shop lights. You may be wondering "How many Watts will actually get dissipated into those two 1000W shop lights?". We can approximate that by assuming 15 Volts is what is coming off the diversion pin which would cause the lights to glow dimly and dissipate about 200 Watts of power.
Many charge controllers can handle 25 Amps or more, but there aren't many that can handle a very high input voltage. This is because most charge controllers use FET transistors to do pulse width modulation. The lower cost FETs can only usually handle 35 to 45V max input voltage. The NC25A charge controller uses a mechanical relay to switch the voltage on and off to the lead acid battery and has a max input voltage of 130 Volts. After searching the internet I have found that there is no other controller selling for this price that can handle that kind of high input voltage.
I took a look at a 35 Amp charge controller made by Sunforce and it can handle a max input voltage of 35 Volts. That kind of controller could easily get blown if you are using it and when the battery gets fully charged, the controller opens up the connection to the battery, and then your pedal power generator voltage shoots up to 40 Volts DC. Then suddenly your Sunforce is permanently damaged. Also the Sunforce does not have the ability to use a diversion load which would act as a braking system to slow your pedaling down.